Variable resistance



Jan. 15, 19 52 A. LILLEY VARIABLE RESISTANCE Filed Jan. 28,.' 1950 1L1) xxx I nvenlor Attorney Jan. 15, 1952 A. LILLEY VARIABLE RESISTANCE 2Sl-lEETS-SHEET2 Filed Jan. 28, l950 O IIHIIIHH F/GS.

I noenlor Attorney Patented Jan. 15, 1952 Application January 28, 1950, Serial No. 141,115 In Great Britain January 28, 1949 9 Claims.

The present invention relates to a variable control device for progressively varying an electrical value such as the resistance of a rheostat or the like and it has for its object to provide a device of simple construction for making sequential or progressive connections and especially for making progressive common connections.

The invention also relates to a variable electrical resistance or rheostat for current control purposes, such as devices for controlling the speed of a series wound fractional horse power motor so as to obtain a progressive control of the speed thereof, which variable; resistance is oi simple and inexpensive construction and is satisfactory and reliable in operation.

In accordance with the present invention a Y contact making device for making progressive electrical connections comprises a plurality of overlying contact springs spaced one from the other and adapted to be flexed progressively into contact one with the other by means of a control member. s

The contact springs or overlying parts thereof are spaced along an axis normal to the springs so that by fiexure in a direction along said axis the springs are brought into progressive common contact. A fixed abutment is preferably provided at one end of the assembly oi springs and the fiexure is effected from the other end of the assembly so that the several springs are positively compressed one against the other progressively to make a good electrical connection and to ensure that contact is made with a wiping action which ensures that the contact surfaces are maintained clean. If desirable raised contact points or studs of any of the materials commonly used for contact purposes, may be provided on the springs, electrical connection being made through the intermediary of such points or studs.

In a preferred construction of a variable resistance or rheostat, a stack of resistance units is assembled and each unit includes a projecting contact spring and the several springs are posititoned one over the other and are flanked on one or both sides by similar contact springs connected to the external circuit, the connections being such that with the springs in their natural positions the resistance in the external circuit is the sum of the resistance of the several units. The control member, which may be a pedal, handle or the like, is adapted to flex the contact springs against or towards an abutment at one end so that some or all of the springs are pressed into common contact, thus varying the resistance in circuit aeggiding to the displacement or the control mem- It will. thus be evident that the invention dispenses with the use of contact studs and a wiper and the constructional and electrical disadvanfages attendant upon variable resistances of the type comprising studs and a wiper.

This invention will further be described by way of example as applied to a variable resistance or rheostat suitable for the control of a series motor and this form of the invention is shown on the accompanying drawings wherein Fig. 1 is a general perspective view of the variable resistance or rheostat,

Fig. 2 is a cross section through the device;

Fig. 3 is an under plan view of Fig. 2,

Fig. 4 is an enlarged side elevation of the stack of resistance units showing the arrangement of the contact springs.

Figs. 5 and 6 are under plan and side views on (VI--VI of Fig. 5) respectively of a modified form of the invention, and

Figs. 7 and 8 are diagrammatic views showing alternative arrangements of the operating or control member which may be used.

In the variable resistance according to the invention shown in Figs. 1 to 4, the resistance wire is wound on fiat formers Ii, preferably mica iormers. The elements so formed are arranged in a. pile or stack, indicated generally at I2, with insulating plates of mica or the like between them and the pile is clamped between end plates I3 with insulating material interposed. One end of each resistance is connected to a blade spring It. The blade springs, which project from the stack, are arranged one above another, but are, of course, in relatively spaced relation as shown best in Fig. 4 owing to the thickness of the elements 01' the resistance wire formers l l and the spacing or insulating plates between the elements. A terminal blade spring I5 is arranged in overlapping relation to the blade spring at one end of the pile and a terminal blade spring I6 is arranged in overlapping relation to the blade spring at the opposite end oi the pile. The assembly comprising the resistance formers H, the insulating spacers; the blade springs l4, Hi, It and the clamping plates I3 is mounted on, say, the base plate or the back plate of a box or housing ll. As shown the stack i2 is fixed to pillars l8 projecting from the base wall of a dished housing I! which is provided with a spring plunger 19 so located that when it is depressed it successively flexes the blade springs l4, l5, it. The remote end plate It forms an abutment towards which the springs H are displaced, the spring l5 not being subject to displacemermt. As a result of such fiexure the resistances or the resistance sections between the terminal blade springs l4 and Ni are successively short circuited, the electric circuits including the flexed blade springs and. therefore, excluding the resistances, when the flexed blade springs are in contact one with another. The several blade springs are thus brought into progressive electrical common contact.

The plunger is preferably provided with an insulated operative end or it may be separated from the blade springs by means of a strip of mica 20 which is also flexed by the plunger. The plunger may be hand-operated as shown in Fig. 6 hereinafter referred to or it may be foot or treadle operated as shown in Figs. 1 and 2. If desired either the plunger or the blade springs directly may be operated by a screw threaded rod 2| as shown in Fig. '7 or by a cam or the like 22 as shown in Fig. 8.

As shown in Figs. and 6 the resistance formers ll may be arranged in a circle, a part cirole. or the like with their blade springs l4 suitably overlapping at one point or along one axis to enable the successive electrical connections to be made and broken, and in such an arrangement some or all of the blade springs may be cranked to ensure that, whilst the formers are in substantially the same plane, the axially aligned parts of the blade springs will normally lie in overlapping but spaced relation as shown in Fig. 6. This permits of the construction of a shallower assembly than is possible with a pile of units.

Owing to the fact that the blade springs are flexed when contact is made and are restored under their spring action when contact is broken, there is a rubbing or wiping action between relatively engaging blades ensuring clean areas at the point of engagement. If desired contact points or studs can be fitted to the blades, such points or studs being of any of the usual materials used for such purposes as dictated by operating requirements.

The variable resistance shown in Figs. 1 to 3 is arranged for pedal control using a sole-shaped pedal 24 pivoted to the outside of the upper wall of the inverted dished housing ll, said upper wall preferably being suitably sloped to provide a comfortable operating position. The under face of the pedal 24 is provided with a knife edge pivot 25 resting in a suitable recess in the housing H. A central stem 26 projecting downwardly from the pivot 25, extends through an aperture in the casing and carries a spring washer 21 held by a split pin 28. A stud 29 projecting from the heel of the pedal 24 extends through an aper ture in the housing and a spring 30 between the inside of the housing and a washer held by a split pin 3!, acts as a return spring for the pedal. The plunger I9 is provided with an enlarged head 32 and is urged upwardly by a spring 33, lodged in a housing 34 extending inwardly into the housing 11, into contact with the under side of the sole of the pedal 24. An adjustable stop screw 35 or the like is provided to limit the return movement of the pedal. On depression of the pedal 24 by the foot, the head 32 is depressed and the plunger I9 formed therewith effects fiexure of the springs l4, 15, It into common electrical contact to short out the resistance units progressively to give a progressive control action, i. e. in the case of a motor control device, to provide a progressive speed control. The housing I! is closed on the under side by means of a base cover 36 and the housing 11 or the cover 36 may be provided with foot pads 31; suit-' able or appropriate electrical connections 38 are brought out through a bushed hole in the housing ll.

What I claim is:

1. A variable electric resistance comprising a stack of parallel flexible contact springs, resistance elements located and clamped between said springs as a unitary stack assembly, each element being connectedto one of said springs and means to variably flex said springs progressively to bring said springs into common electrical contact according to the degree of flexure.

2. A variable resistance, comprising a dished housing, a displaceable operating member externally of said housing, a stack of resistance units in said housing, insulating means between said units, a contact spring electrically connected to each unit, the several springs having portions lying normally in mutually spaced overlying relation and the resistance units lying between said springs as a unitary stack assembly, an axially movable plunger in said housing positioned to engage and flex said overlying springs into progressive common electrical contact and an operative connection between said operating member and said plunger.

3. A variable resistance according to claim 2 wherein said units are flanked by a contact spring connected to an external circuit.

4. A variable resistance according to claim' 2 wherein said units comprise insulating strips wound with resistance wire, each connected electr'ically with one of the springs.

5. A variable resistance according to claim 2, wherein the operating member comprises a member pivoted on said housing, spring means tend ing to return said member to an inoperative position, said plunger being spring returned to normal position and displaceable axially by said member on displacement thereof from its inoperative position, the several springs being positioned for displacement into common electrical contact and electric connection means connected to said units so that progressive displacement of said operating member and plunger to flex said overlying springs into progressive common electrical contact effects a progressive reduction of the resistance offered through said connection means.

6. A variable resistance according to claim 2 wherein said stack is clamped between end plates with the contact springs projecting therefrom.

" '7. A variable resistance according to claim 6 wherein one end plate is extended to act as an abutment for the contact springs, flexure thereof being progressively towards said abutment.

.8. A variable resistance according to claim 7 wherein a strip of insulating material is inter posed between said abutment end plate and be- -tending longitudinally between the elements to space said springs one from the other, said springs being each connected to an element and extending therefrom at one end, rigid end plates insulated from and between which the springs, elements and plates are clamped, one end plate being extended to form an abutment, the in- 5 sulating plates adjacent and within the end plates REFERENCES CITED being extended with the extended ends of said contact springs and the abutment, and the ext 8 g i f i are of record in the tended end thereof remote from the abutment being flexible, electrical current supply connections 5 UNITED STATES PATENTS connected to remote springs, and means acting on Number Name Date said flexible end to variably flex the same and the 1,952, 79 Leveen Man 7 934 extended ends of the contact springs progressively toward said abutment to bring said extended FOREIGN PATENTS ends'of the springs with a wiping action into 10 Number Country Date common electrical contact according to the de- 572,630 Great Britain Oct. 17, 1945 ree of fiexure to progressively cut out the resistance elements.

ARTHUR LILLEY. 

